The present invention relates to a non-contact data carrier system, for communicating by use of a radio wave, for uses for verification of various IDs, financial trading and control of a door lock of a car, and a non-contact data carrier used for the same.
A non-contact IC card as an example of the non-contact data carrier has a convenience that it is unnecessary to insert the non-contact IC card into a slot of a reader/writer as well as features of normal IC cards having a large storage capacity and a high-degree security function. Therefore, the non-contact IC card is a product of which a great market can be expected not only as a commuter ticket of public transportation and a ticket for a ski lift but also as a room entry/exit card for opening or closing a door and a card for electronic money. Such a non-contact IC card performs information transmission and reception with a question unit by use of a medium such as a radio wave. Power necessary for operation of a control circuit and a memory of the non-contact IC card is obtained from a battery incorporated in the card or by rectifying, by a radio wave transmitted from the question unit, an induced current generated due to mutual induction of a coil provided in the non-contact IC card.
FIG. 7 is a block diagram showing the configuration of a conventional non-contact IC card which operates on power supplied from a battery 29. A main circuit unit 13 of the non-contact IC card comprises a reset circuit 5, a demodulation circuit 6, a modulation circuit 7 and a memory 12. The main circuit unit 13 further comprises a control circuit 11 for controlling the above-mentioned circuits and performing reading from and writing to the memory 12 in accordance with the contents of a signal transmitted from a question unit (not shown). A transmitter-receiver 1 comprising an antenna and a tuning circuit (both are not shown) receives a radio signal transmitted from the question unit. A carrier signal detection circuit 3 compares the level of the received signal and a reference level preset in the carrier signal detection circuit 3. When the level of the received signal is higher than the reference level, a switching circuit 8 goes into on state, so that power is supplied from a battery 29 to the main circuit unit 13. As a result, the non-contact IC card operates. When the level of the received signal is not higher than the reference level, the non-contact IC card does not operate and goes into sleep state which is the state only to receive and detect a signal which will be again transmitted from the question unit.
In the non-contact IC card having the switching circuit 8, power is supplied to the circuit components only when a carrier signal from the question unit is detected. Therefore, when no carrier signal is transmitted from the question unit, that is, when information transmission and reception is not performed between the non-contact IC card and the question unit, only the carrier signal detection circuit 3 consumes power, so that power consumption is reduced.
The above-mentioned non-contact IC card uses an internal battery 29 as the power source and the power necessary for operation of the non-contact IC card is supplied from the battery 29. On the other hand, in a non-contact IC card which uses induced electromotive force generated at a coil incorporated in the non-contact IC card, rectified induced-electromotive-force is stored and the stored force is used for operation of the non-contact IC card. Therefore, the induced electromotive force generated in the coil decreases corresponding to increase of the distance between the non-contact IC card and the question unit. In order to prevent the induced electromotive force from decreasing, it is necessary to use the non-contact IC card in the proximity of the question unit at the time of communication.
That is, in the latter non-contact IC card, the longer the distance between the question unit and the non-contact card is, the lower the value of the induced electromotive force is, so that it is difficult to ensure the power necessary for operation. On the contrary, in the former non-contact IC card, since stable power is supplied from the battery 29, long-distance communication can be performed.
Generally, the convenience of the non-contact IC card is influenced by a communication-possible distance between the question unit and the non-contact IC card. By increasing the communication distance between the non-contact IC card and the question unit, the non-contact IC card can be used at a position remote from the question unit, and thus the convenience is improved. The non-contact IC card in which power is supplied from a battery is excellent in convenience because a long communication distance can be ensured compared with the non-contact IC card using the induced electromotive force.
However, since the battery is required for operation, the non-contact IC card becomes inoperable when the capacity of the battery is low, that is, when the battery is exhausted. As described above, when the non-contact IC card is in sleep state, only the carrier signal detection circuit 3 is actuated for detecting a signal from the question unit. Therefore the power consumption is reduced. However, slight power is still consumed. Consequently, the battery is exhausted when the non-contact IC card is used for a long time. Normally, the non-contact IC card does not have means for displaying the remaining capacity of the internal battery, so that it is impossible for the user of the non-contact IC card to predict battery exhaustion. For this reason, the non-contact IC card is hardly used for important work or for recording important data.
When the battery is exhausted, the use of the non-contact IC card cannot be continued unless a replacement battery is at hand. Even if a battery is available, a tool such as a screwdriver is necessary for battery replacement, so that it is very difficult to replace the battery in a short time to use again the non-contact IC card.
An object of the present invention is to prevent a trouble caused by battery exhaustion of the non-contact IC card while maintaining the convenience that long-distance communication can be performed.
Another example of use of a conventional non-contact data carrier will be described hereinafter.
Conventionally, a door lock of a car employs a system for locking or unlocking the door by inserting a key into a key cylinder provided at the door and turning the key either leftward or rightward. In recent years, in order to simplify such locking or unlocking by use of a key, a wireless door lock system, namely, so-called keyless entry system has become widespread for locking and unlocking not only a door but also a trunk lid without the use of the key. In the keyless entry system, a locking or unlocking instruction is transmitted to a locking device for the door or the trunk lid from a position remote from it. The locking or unlocking instruction is given by use of light or a radio wave. For example, by pressing a push button 31 provided on a key terminal 30 as shown in FIG. 8, a key ID number is transmitted to the locking device of a vehicle. The key ID number is verified by a terminal device mounted in the vehicle. As a result of the verification, when the key ID number coincides with the key ID number of the vehicle, door locking or unlocking is performed. According to this configuration, even at nighttime or in an indoor parking lot where the keyhole of the key cylinder is not easily found because it is dark, door locking or unlocking can be easily performed without the key being inserted into the key cylinder. Recently, many vehicles have employed this system for the purpose of increasing their added values.
In this keyless entry system, it is necessary to take out the key terminal 30 and transmit the key ID number by pressing the push button 31 toward the vehicle every time door locking or unlocking is performed. Although it is unnecessary to look for the keyhole in order to insert the key into the key cylinder, when the user""s both hands are taken up by baggage or when the user puts up an umbrella at the time of rain, it is necessary for the user to put down the baggage or the umbrella before taking out the key terminal 30 and pressing the push button 31 to perform key locking or unlocking. Thus, the conventional keyless entry system is still inconvenient.
Data of the key ID number used in the above-described system is transmitted from the key terminal to the vehicle-mounted terminal device as a coded binary signal. Therefore, the key ID number data can be fraudulently obtained by disassembling the key terminal and analyzing it in detail. Further, the coded signal, which is comparatively simple, can be read by a cryptoanalysis apparatus. The key ID number can also be obtained by replicating the signal. The terminal device controlling door lock condition determines that an access is made by an authorized key terminal when the received key ID number coincides with the key ID number of the vehicle, and locking or unlocking is performed. It is difficult to adopt a configuration for denying an access from a key terminal transmitting a fraudulently obtained ID number. Thus, the conventional keyless entry system is defective also in security.
The key terminal incorporates a battery and uses it as the power source when transmitting the key ID number data. When the battery capacity is low, that is, when the battery is exhausted, the Key ID number data cannot be transmitted from the key terminal. Under such a state, door locking or unlocking by the keyless entry system cannot be performed, so that it is necessary to insert the key into the key cylinder to lock or unlock in a manner similar to the conventional door lock.
The present invention is intended for solving the above-described conventional problems, and provides a non-contact data carrier system applied to control of a door lock of a car in which security and convenience of the keyless entry system are maintained without use of a key to lock or unlock the door.
A non-contact data carrier of the present invention comprises transmission-reception means for receiving a carrier signal from a question unit and transmitting transmission data to the question unit, carrier signal detection means for detecting the carrier signal, a demodulation circuit for demodulating the carrier signal, a modulation circuit for modulating the transmission data to be transmitted to the question unit, a memory for holding data, and a control circuit for controlling the modulation circuit and the memory, the control circuit receiving an output of the demodulation circuit. The non-contact data carrier further comprises switching means for supplying power of an internal battery to a main circuit unit when the carrier signal is detected, electric-supply means for rectifying the carrier signal and generating a voltage, and electric-supply switching means to which an output of the electric-supply means and an output of the switching means are input. The electric-supply switching means compares a voltage value of the battery and a voltage value of the electric-supply means, and switches between the battery and the electric-supply means.
According to the above-described configuration, when the battery is capable of supplying power, power is supplied from the battery, so that long-distance communication is realizable. In case of battery exhaustion, power is supplied by induced electromotive force from the question unit by using the non-contact data carrier in the proximity of the question unit, so that the function of the non-contact data carrier can be maintained.
Moreover, in the non-contact data carrier according to another aspect of the present invention, the level of the carrier signal and a predetermined reference level are compared with each other by the carrier signal detection means. When the level of the carrier signal is higher than the reference level, the switching means goes into on state. When the switching means is in on state, the voltage value of the battery and the value of the voltage generated by the electric-supply means are compared. When the voltage value of the battery is higher than the value of the generated voltage, power of the battery is output to the main circuit unit by the electric-supply switching means.
Moreover, the voltage of the electric-supply means obtained by the received signal and the battery voltage are compared with each other. When the voltage obtained by the received signal is higher than the battery voltage, the power supply from the battery is stopped. When the voltage obtained by the received signal is lower, power is supplied from the battery. Thereby, the power consumption of the battery of the non-contact data carrier is reduced, the battery life is increased.
A non-contact data carrier system of the present invention comprises a non-contact data carrier held by a user of a car, and a question unit mounted in the car. The question unit performs information transmission and reception with the data carrier. The non-contact data carrier stores information such as an ID number therein and performs processing according to information transmitted from the question unit. The question unit comprises switching means for switching operation condition and lock control means for controlling door lock means based on a control signal from the question unit. Since the control of door lock means is performed based on the information such as an ID number stored in the non-contact data carrier, security is maintained.
In the question unit of the non-contact data carrier system of the present invention, an antenna is pasted on a front door of a car, preferably, on a driver side window pane, or an antenna is printed on a window pane. Communication with the non-contact data carrier is performed through the antenna. The switching means for switching operation condition of the question unit is disposed in the proximity of the antenna and comprises a touch switch circuit and a lock control unit. A sensor of a touch switch is provided on the door lever of the driver""s seat side, and communication between the non-contact data carrier and the question unit can be performed only when the touch switch is on. Door locking and unlocking can be performed only by the door lever being touched by the user holding the non-contact data carrier. As a result, the user""s convenience greatly improves.
Further, by providing the timer circuit in the switching means, even when on state of the touch switch is continued for a long time by mischief and the like, the question unit can be brought into wait state after a predetermined time period has elapsed according to counting by the timer circuit. Thereby, not only power consumption due to continuous transmission of signal from the question unit can be reduced but also frequent switching of door lock condition, that is, frequent repetition of locking and unlocking can be prevented.
In the non-contact data carrier system according to another aspect of the present invention, when the user brings the switching means into on state, the question unit transmits a signal to the non-contact data carrier. The question unit determines the contents of the signal returned from the non-contact data carrier and performs the control of the door lock by the control means. The signal returned from the non-contact data carrier is produced based on information transmitted from the question unit and the ID information stored in the non-contact data carrier. The returned signal includes information on the question unit, therefore it is difficult to obtain the data necessary for door lock control even if attempt is made to analyze the internal structure of the non-contact data carrier. Thus, the non-contact data carrier system provides high confidentiality.